Answer to Question #270866 in General Chemistry for Yai

Question

2. How many milliliters (mL) of 0.10 M NaH solution are required to completely neutralize 20.0 ml of a 0.175 M solution of HyPO, to the phenolphthalein end point? Na0H (aq) H,PO, (ag) Na,PO, (aq) + H,O (0) unbalanced equation

Answer 1

Write down the balanced reaction first

3NaOH + H3PO4 makes Na3PO4 + 3H2O

Given 0.10M NaOH (0.10mol/lit NaOH)

0.2M H3PO4 ( 0.2 mol/lit H3PO4)

15 ml of H3PO4 or 0.015 lit of H3PO4

Find volume of NaOH needed to neutralize the solution

Relate moles of H3PO4 with the moles of NaOH with the helps of coefficients in front of NaOH and H3PO4 seen in balanced equations.

moles ↔ Litre use definition of molarity (moles/litrs)

Start with what is given for H3PO4

0.015 lit of H3PO4 x 0.2 moles of H3PO4 / lit of H3PO4 x 3 moles of NaOH/1 mole of H3PO4 x lit of NaOH/0.1 mol of NaOH = 0.09 lit or 90 ml.